The present invention relates to a combustion-type power tool, and more particularly, to such power tool capable of driving a fastener such as a nail, an anchor, and a staple into a workpiece.
In a conventional combustion-type driving tool such as a nail gun, a mixture of air and gaseous fuel injected into a combustion chamber is ignited by a spark at an ignition plug to cause gas expansion in the combustion chamber, which in turn causes a linear momentum of a piston. By the movement of the piston, a nail is driven into a workpiece. Such conventional combustion-type nail gun is described in U.S. Pat. No. 5,197,646 and Japanese Patent Publication No. H03-25307.
According to the conventional combustion-type power tool, a temperature of an entire tool including a gas canister is increased by heat generated upon combustion in a combustion chamber, particularly upon repeated operation, for example, continuous nail driving operation. As a result, an inner pressure of the gas canister will be increased thereby increasing an injection rate of the combustible gas. In the combustion-type power tool, air-fuel mixture can be ignited if gas density in the combustion chamber (amount of combustible gas per an entire inner volume of the combustion chamber) is within a predetermined range. If the injection amount of the combustible gas is increased, i.e., if density of the combustible gas is increased, ignition does not occur, or sufficient expansion capable of driving a nail into a workpiece cannot be provided due to insufficient ignition.